EASY!

Well let me explain to you how to do it...

First you have to find a good quarterpipe that you are comfortable with so you won't feel weird every time you ride it.

After that it is the best to know how to do a backflip because it is almost the same movement and your body position will be upside down so it is better to get used to it before doing it on a quarterpipe.

The easiest way to start learning them is if you have a foam pit with a normal jump. If you have one, then just start with the flip and then slowly try to turn little bit to your side and twist your body to the side you prefer. Your flip will start getting crooked until you get it 180 degrees. If you have a foam pit with a quarterpipe then it's better to try it straight away into the foam from the quarterpipe. If you have one, just go to the side that you prefer and try to pump out straight in the air from the quarterpipe with a slight turn to your side, so when your front wheel goes up then do aggressive turn with your head down and to your side and concentrate your body, don't be scared and look for your landing. 

When you learn it in the foam it is time to try it on a quarterpipe...I know that doesn't sound easy but it really is.

So:

Step Zero: be brave!

Step One: ride straight with a speed that allows you to do air from a quarter,.. not too fast!

Step Two: when your wheels start climbing up the quarter just make a small turn to your side, not to much because it will spin you in the wrong way.

 

Step Three: when your wheel starts going off from the quarter, pump up in the air and slowly lean back like you wanna do a flip

Step Four: when your front wheel is off just do an aggressive turn with your head down and to your side and lead your body in the same direction your head goes.

Step Five: you just have to stay concentrated and wait until spin/flip/flair is finished :)

Step Six: look for your landing and push your bike on it.

Step Seven: land it!

Step Eight: repeat it few times.

Step Nine: go celebrate with your friends!!

Cheers!